The invention relates to a plant with high temperature fuel cells and to methods for operating the plant.
High temperature fuel cells, for example of the SOFC type (xe2x80x9cSolid Oxide Fuel Cellxe2x80x9d), enable an exploitation of the energy which is converted by the fuel cells in the operation of a building infrastructure. In this both the electrical energy which is produced as a result of electrochemical processes and the thermal energy which arises in the form of hot exhaust gases of the processes are used. If the building infrastructure is provided for a climate in which the weather conditions, in particular the ambient temperatures, vary in a marked fashion, then it is necessary at times to give off surplus heat to the surroundings. If fuel cells of the SOFC type are used, then the temperature of the exhaust gas is so high that the exhaust gas must not be expelled directly via a chimney into the surroundings in order to eliminate surplus heat. At these high temperatures, damage to the chimney could result; the hot exhaust gas would also be a source of danger for the environment.
Plants for the simultaneous production of electrical and thermal energy are known from EP-A 0 823 742. In these plants a surplus amount of heat which arises with the exhaust gases can be utilized by means of thermal engines. Possibilities of use of this kind are however often complicated and expensive, so that it is economically more advantageous to eliminate surplus heat in that it is emitted unused to the surroundingsxe2x80x94xe2x80x9cdisposed ofxe2x80x9d.
It is an object of the invention to create a plant with high temperature fuel cells which permits the electrical and thermal energy requirement of a building infrastructure to be covered and the surplus heat which arises from time to time to be emitted to the surroundings without parts of the building infrastructure being damaged or the environment being endangered.
The plant contains high temperature fuel cells which form a battery in which electrochemical reactions can be carried out with a fuel and a gas containing oxygen while producing an electrical current and a hot exhaust gas flow which transports waste heat. The plant comprises a device with the following components:
a circulation with a heat carrier medium,
a first heat exchanger for the exhaust gas flow in which a portion of the waste heat can be transferred to the heat carrier medium,
at the output of the heat exchanger a discharge conduit for the exhaust gas flow which leads to a chimney, with it not being permitted for the exhaust gas temperature in the chimney to exceed a predetermined value, and
at least one heat sink, in particular in the form of a further heat exchanger, in which the waste heat which is transferred to the heat carrier medium can be removed from the circulation at least partly as surplus heat when required, with it not being possible for the surplus heat to be used either for room heating and/or utility water heating or for another useful purpose.
In the following the invention will be explained with reference to the drawing.